A jack is one of the commonly used tools in our daily life. It is typically used to lift a load a preset lift distance with smaller forces than that required to lift it directly. Its input piston, which has a small surface area to move with a small force, pushes the hydraulic oil into the output cylinder, thus driving the output piston, which has a larger surface area to lift the load. In accordance with the Law of Conservation of Energy, the input piston travels a much larger distance than the output piston does. As a result, it is typically necessary to pump the input piston repeatedly. In this process, each pump cycle of the input piston results in the same lift distance of the load, being independent of the magnitude of the load. As a result, in the case of an idle, or no, load, light load, or heavy load, it is necessary to pump the input piston repeatedly. The load goes up very slowly even if the load is small. This wastes both time and effort.
To solve the above-identified problem, a hydraulic jack described in Chinese Pat. No. 99209440.2 adopts a double-jacket piston structurexe2x80x94a smaller piston is located within a larger one of the input cylinder. There are two pressurized surfaces in the input cylinder. In the case of an idle load, the jack uses its larger piston to pump oil to increase the quantity of hydraulic oil pumped into the output cylinder, thus making the lift distance for each pumping cycle larger and thus increasing the overall lifting speed. In the case of a heavy load, the jack then uses its smaller piston, which is equivalent to a piston of a conventional jack. This configuration can therefore yield a saving of effort relative to a conventional jack.
Although the double-jacket piston structure solves the problem of wasted time and effort in the case of an idle load, a problem can arise during the process of changing from a small to a large load, when it is used to lift a light load. Besides, if this kind of jack is used to lift a small weight, it still needs the same number of pumping cycles as when it is used to lift a heavy weight, and the problem of wasted time still remains. Moreover, since it adopts a structure with a smaller piston in a larger one, the manufacture process and structural strength are limited, thus the area ratio of the pressurized surface in the case of an idle load and a heavy load is relatively small. As a result, there is little improvement in lifting speed in the case of an idle load. Practical application indicates that this jack still needs many pumping cycles to reach the necessary height; its efficiency is thus not high.
There is another type of hydraulic jack, which opens a blind hole in the middle of the piston of its output cylinder. An oil pipe is inserted into the blind hole. In the case of an idle load, when the piston of the input cylinder is pressed, the hydraulic oil flows into the blind hole via this oil pipe to push the piston for a rapid lift against the end face of the blind hole. In the case of a heavy load, part of the hydraulic oil opens a sequential valve and flows into the output cylinder. The force applied against the ring type surface of the piston of the output cylinder by the oil which flows into the output cylinder together with that applied against the end face of the blind hole by the oil which flows into the blind hole, jointly lift the load at a slow speed. Since the blind hole has a small area to receive force, the lift speed of the jack is very fast in the case of an idle load. Generally, the piston of the output cylinder can reach the height with only one or two pump cycles or strokes. On the other hand, in the case of a heavy load, since the whole end face of the piston of the output cylinder is taken as the area to receive force, the purpose of saving effort is also achieved.
However, it is found from practical application of this type of hydraulic jack that it cannot meet the requirements as expected above. The reason is that when the hydraulic oil is pressed into the output cylinder via the oil pipe, the piston of the output cylinder goes up rapidly; the pressure in the ring type cavity of the output cylinder goes down swiftly to suck hydraulic oil from the oil tank. However, since the piston moves relatively fast and the area of the ring type cavity changes very much, the sucked hydraulic oil cannot fully fill up the ring type cavity, resulting in a phenomenon of inefficient oil suction. Since there exists some air in the ring type cavity of the output cylinder, when the output cylinder starts to lift load, the load applies forces to the piston and makes the piston fall back a certain distance, thus reducing the speed of lift of the load. Moreover, after repeated pump cycles, the air held in the ring type cavity of the output cylinder flows into the input cylinder via the oil path, bringing about the same phenomenon of inefficient oil suction for the input cylinder; this reduces the lift distance for each pump cycle, and moreover the lifting efficiency. Additionally, this type of jack has also another disadvantage. Since the lifting force comes from the joint effort of the hydraulic oil flowing into the blind hole via the oil pipe and that flowing into the ring type cavity of the output cylinder via the one-way valve, the area of the blind hole and that of the ring type cavity changes at each pump press, it is necessary to ensure a balance between the pressures from the hydraulic oil flowing into the ring type cavity and that flowing into the blind hole to achieve a steady movement of the output piston. Unfortunately, it is very difficult to accomplish such a result in practical batch production process. As a result, when the controlled hydraulic oil enters the ring type cavity and is locked there, cracks of the thin-wall oil pipe can occur often owing to a large pressure in the blind hole. This results in low rate of finished products for this type of jack and thus increases its production cost.
It is an object of the present invention to provide a multilevel speed regulation method for a jack, which enables the jack to transfer between different lift speed levels in the case of different loads and avoid the phenomenon of time waste in the case of an idle load and a light load, so that the objectives of saving both time and effort and increasing lifting efficiency are achieved.
It is also an object of the present invention to provide a multilevel speed regulation jack, which can transfer between different lift speeds in the case of different loads, so that the lifting efficiency of the jack is enhanced.
The purposes of the present invention are achieved by using the following technical arrangement. In the multilevel speed regulation method and system for a jack, a hydraulic speed regulation line is arranged between the input and output cylinders, which includes at least two parallel hydraulic sub-lines to form a hydraulic speed regulation line with at least three speed levels. It takes the pressure applied by the output cylinder against the load as its control signal to control the opening and closure of the hydraulic sub-lines and their combination at different speed levels in the hydraulic speed regulation line.
The hydraulic speed regulation line comprises, in one implementation, three or more than three parallel hydraulic sub-lines, and, with one hydraulic sub-line added, two speed levels are added accordingly. A control valve is set in the hydraulic sub-lines to control the opening and closure through the control signal taken from the load pressure. The opening pressure of the hydraulic sub-lines is set in sequence and opens with the increase of the load.
In general, according to another aspect, the invention features a multilevel speed regulation jack, which includes at least one input cylinder and one output cylinder, and one oil path interconnecting the input cylinder and output cylinder, wherein there is a hydraulic speed regulation line connected in series between the input and output cylinders that provides at least three speed levels. This hydraulic speed regulation line comprises at least two parallel hydraulic sub-lines and takes the load pressure of the output cylinder as its control signal to control the opening and closure of the hydraulic sub-lines or their combination at different speed levels.
In one embodiment, the hydraulic speed regulation line comprises three or more parallel hydraulic sub-lines. Control valves are set in the hydraulic sub-lines to control the opening and closure through the control signal taken from the load pressure. The opening pressure of the hydraulic sub-lines is set in sequence and opens with increases of the load. The control valve set in the hydraulic sub-lines can be either a one-way valve or a sequential valve.
The operating process and principle of the present invention is: in case of an idle load or a very light load, when the piston of the input cylinder is pressed, the hydraulic oil is pumped to the input cavity of the speed regulation cylinder in the hydraulic sub-lines at a high speed level to push its piston to press the hydraulic oil in the output cylinder, and with the opening of the control valve, the hydraulic oil flows into the output cylinder and then pushes the piston of the output cylinder to lift the load rapidly at the first speed V1. When the piston in this input cylinder is raised, the piston in the speed regulation cylinder returns to its original position under the forces from the flexible restoring mechanism, and meanwhile, the output cavity connected to the oil storage cylinder sucks oil and fills up the output cylinder. When the piston in the input cylinder is pressed once again, then the above process repeats. In this process, since the end face of the piston in the input cavity of the speed regulation cylinder is smaller than that of the piston in the output cylinder, the lift distance to lift the load each time is increased and also the lifting speed enhanced. With the increase in load against the output cylinder, and when the pressure of the input oil becomes larger enough to open the control valve in the next hydraulic sub-line, this control valve opens. Part of the hydraulic oil now pushes the piston of the speed regulation cylinder at the next speed level, and delivers the hydraulic oil in the output cavity of the speed regulation cylinder at the next level to the output cylinder, and thus pushing the piston to lift load at the second speed V2. Since the difference between the areas of the input cavity and output cavity of the speed regulation cylinder at the next level is less than that of the high-speed hydraulic sub-line, then the lift speed V1 is less than V2. As a result, in accordance with the Law of Conservation of Energy, the capacity to lift load increases for the same input pressure. With the increase of load, the back pressure thus produced closes the control valve in the high-speed hydraulic sub-line, and the hydraulic oil pumped by the input cylinder is fully applied to the speed regulation cylinder at the next level to drive the piston to deliver the hydraulic oil in the output cavity to the output cylinder, thus the piston in the output cylinder lifts load at the third speed V3. As above, the third speed V3 is less than the second speed V2. However, the lifting capacity in this case increases further, being capable to lift the load in this stage. As the load increases, the control valve in the low-speed hydraulic sub-line opens. Now part of the hydraulic oil is pumped directly to the output cylinder via this hydraulic sub-line and forces the piston of the output cylinder to lift the load at the forth speed V4. Still as above, the forth speed V4 is less than the third speed V3. However, the lifting capacity in this case increases still further, being capable enough to lift the heavier load in this stage. As the load increases still further, the sequential valve of the hydraulic sub-line at the next level closes under the force from the back pressure, the hydraulic oil pumped by the input cylinder is fully delivered to the output cylinder via the low-speed hydraulic sub-line and forces the piston of the output cylinder to lift load at the fifth speed V5. Still as above, the fifth speed V5 is less than the forth speed V4. However, the lifting capacity in this case reaches its maximum value. In such a case, since the hydraulic oil delivered into the output cylinder is directly pumped from the input cylinder, its operational principle is the same as that of a conventional jack.
In the above operating process of this invention, the transfer between various lifting speeds is automatically done with the change of the load. With the same effort each time, a load is lifted that increases continuously by regulating the speed without a need for any additional operations. This invention enhances the lifting efficiency and features simple and fast operation, achieving the purposes of saving both time and effort. Besides, in the speed regulation process, except that the input cylinder absorbs oil as does a conventional jack when the low-speed hydraulic sub-line between the input cylinder and output cylinder of the last hydraulic sub-line opens, there is no oil added in the input cylinder at all other speed levels. It only takes the hydraulic oil as a medium of pressure transfer to transfer the pressure applied against the piston of the input cylinder. As a result, it does not involve the problem of inadequate absorption of oil in the input cylinder as occurs with the present technology. Furthermore, the absorption process of oil after the input cylinder directly pumps hydraulic oil into the output cylinder via the low-speed hydraulic sub-line does not exist; it can do as well as a conventional jack does. All of the above works to avoid the phenomenon of filling back during lifting and thus ensures the efficiency of the load lifting process.
According to one embodiment, an overload protection device is provided for this invention. When the load that the output cylinder is lifting exceeds the pressure that the jack can bear, the high-pressure oil in the input cylinder will open the overflow valve for pressure relief. The hydraulic oil flows back into the oil tank via the overflow valve, and therefore prevents damage to the jack.
In the jack in this invention, several more hydraulic speed regulation sub-lines can be connected in parallel to the hydraulic sub-lines connected to the input cylinder. With one hydraulic sub-line added, two speed levels are added accordingly, which makes the jack""s speed adjustable at multi-levels during its operation. In terms of its design, different specifications of the jack can be worked out according the magnitude of the load so that in application, different jacks of different specifications can be selected, depending on the specific requirements. When it is used to lift relatively smaller loads, a jack with relatively fewer speed levels can be selected. On the other hand, when it is used to lift a relatively larger load, a jack with relatively more speed levels can be selected. Since the jack from the present invention demonstrates different lifting capacities when it is working at different speed levels, it is, in fact, equivalent to a conventional jack with the corresponding lifting capacity. The effect when it is working at different speed levels in parallel, it is equivalent to several jacks of different specifications working at different load ranges with the increase of the load when it is used to lift load. As a result, the present invention incorporates functions of several conventional jacks of different specifications into one jack, and automatically regulates its speed in correspondence with the load changes. It is simple and convenient in lifting operations with enhanced lifting efficiency and equipment utilization rate.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.